Fresh install of macOS Big Sur ... always tries to reinstall the older macOS

Hello,

When trying to perform a fresh install of macOS Big Sur on my MacBook Air 2019 I only can reinstall the original macOS (Mojave) version.

I have a USB stick with Big Sur on it (I already used this USB to install my other Macs without any issue), boot my MacBookAir by holding down the Option key when powering on. I see appearing the Big Sur USB, clicking on this I can select Disk Utility, ... but to install macOS I only have the option to Reinstall macOS (with Mojave).

Why can't I fresh install my MacBookAir like I could with my other Macs?

Thanks.